This invention pertains to the valve art and, more particularly, to ball valves.
The invention is particularly applicable to a new and improved seat assembly for a ball valve of the type having a so called "floating ball" and will be described with particular reference thereto. However, it will be appreciated that the invention is capable of broader applications and may be advantageously employed in other environments.
Prior ball valve constructions as disclosed in the commonly assigned U.S. Pat. Nos. 3,894,718 and 4,410,165, the teachings of which are incorporated hereinto by reference, include a resilient seat ring construction employing disc springs for urging the seat rings into sealing contact with a ball member. The ball member is mounted for a slight amount of free movement or axial shifting when the ball member is in a valve closed position under fluid pressure conditions. Shifting of the ball member enhances downstream seat ring engagement therewith.
Typically, these valve constructions are entirely satisfactory for low and intermediate fluid pressure conditions. However, at more elevated fluid pressure conditions, especially with elevated temperatures and abrasive media, the resilient seat ring assemblies have been found to be less effective. Instead, high fluid pressure applications have generally required use of metal seats of various constructions. Certain operational problems encountered with prior metal seat designs have been remedied to some extent by matched lapping of the seat ring and ball valve member. Other remedial designs have provided a hard coating on the sealing surface of the seat ring for inhibiting degradation of the remainder of the seat ring assembly.
Although these prior arrangements have met with some success, they necessarily result in special manufacturing requirements in order to maintain close tolerances and adequate sealing in high fluid pressure conditions. Specifically, both the matched lapping and appication of a hard coating add significant costs to the valve, particularly when viewed from the standpoint of the relative benefits derived therefrom.
Additionally, other prior constructions have captured the metal seat rings between a counterhore formed in the central passage of the valve body and an end member, thereby retainingly engaging the seat ring assembly in contacting relation with the ball member. In this type of construction, the seat rings are limited in their degree of movement within the valve chamber which, in turn, limits the ability of the seat ring assembly to conform to the outer circumferential surface of the ball member. The inability of the seat ring assembly to flex for obtaining enhanced sealing engagement with the ball member, either upon valve assembly or during free movement or axial shifting of the ball member, limits sealing capabilities under extreme fluid pressure conditions.
Accordingly, it has been considered desirable to develop a new and improved seat assembly constructed from a high strength material which would facilitate better seat ring flexure and sealing at elevated fluid temperature and pressure conditions.
The subject invention is deemed to meet these needs and others in an efficient, economical manner for providing a valuable advance to the state of the art.